Why? None of that will stop a virus that is written to steal your coins.
I think we have to accept that there's no way to use BitCoin securely from a malware infected computer at the moment and there probably won't ever be. If you want to use BitCoin from a possibly compromised machine you need to do it via a 2-factor protected mybitcoin style site in which the wallet is held remotely and transactions are signed using some kind of electronic signing calculator (see CAP).
Right now, even if the Bitcoin client is not running, your wallet is stored unencrypted. There's no reason to make it that
easy to steal your wallet. The changes I proposed would allow the client to handle multiple wallets in a manner that is more secure than the current handling of a single wallet. For instance, I've been working on a wallet manager that stores the wallet(s) encrypted, and only decrypts it to launch the Bitcoin client. The problem with this is that you cannot run as a node while also keeping your wallets securely stored. (Aside... I just realized a potential workaround - let the client create a new wallet instead of using one of the user's.)
There's no way to do anything securely. Security is not a binary value. The point is enhancing the default security level that the Bitcoin program provides.